Amid concerns over global warming, and forecasts of both the depletion of non-renewable energy sources and rising power demand, suppliers of energy are increasingly seeking alternative primary sources of energy. One such source of energy is solar energy, and one way of utilizing solar energy is with a solar thermal power plant.
One type of solar power plant utilizes a “radiation concentrator collector” which concentrates the solar radiation by focusing it onto a smaller area, e.g., using mirrored surfaces or lenses. In this system, a reflector, which is typically parabolic, receives and reflects (focuses) incoming solar radiation onto a radiation absorber, which is formed as a tube. The tube radiation absorber is concentrically surrounded by a treated glass enclosure tube to limit the loss of heat. The collector system further includes means to track the sun.
To minimize the loss of heat through convection and conduction and to improve the solar radiation collection efficiency, the space between the tube radiation absorber and the glass enclosure tube is evacuated to very low pressure.
The tube radiation absorber is made of metal with a coating having a high solar radiation absorption coefficient to maximize the energy transfer imparted by the solar radiation reflecting off the reflector. A thermal fluid constituting a heat transport medium, which is typically a liquid such as oil, flows within the tube radiation absorber.
The thermal energy transported by the thermal fluid is then is used to power a steam-electric power plant to drive one or more turbines, in order to generate electricity in a conventional way, e.g., by coupling the axle of each of the turbines to a generator.
The thermal fluid powers the steam-electric power plant by transferring thermal energy thereto. Although the steam-electric cycle is more efficient at high temperatures, at a particular high temperature threshold, some thermal fluids may dissociate or otherwise break down or become less effective at transferring heat. Accordingly, such solar thermal energy generating plants are typically limited to operate at temperatures below this threshold, which for some thermal fluids may be in the region of about 400° C.